1. Field of the Invention
The invention pertains to carboxylic acid functional organopolysiloxanes of defined structure, which are preferably self-emulsifiable, either as such, or in the form of salts thereof. The organopolysiloxanes contain pendent, regularly spaced carboxylic acid groups or salts thereof, and in-chain ester linkages.
2. Description of the Related Art
Emulsions and dispersions of polyorganosiloxanes (“silicones”) have a myriad of uses. For silicones bearing only non-polar and/or non-functional groups, e.g. polydimethylsiloxanes, these exceptionally hydrophobic silicones are not emulsifiable nor dispersible (when solid) by themselves in aqueous compositions. In order to form emulsions or dispersions, surfactants are added, and the silicones are then emulsified, generally under high shear. A wide variety of silicone particle sizes can be created, depending upon the shear exerted upon mixing, the amount and type of surfactant, etc. Such emulsions (hereinafter including dispersions except as noted) are well known in the art and are available commercially from numerous sources. The surfactants used may be non-ionic, Gemini-type, anionic, cationic, zwitterionic, etc. Mixtures of surfactants, e.g. mixtures of non-ionic surfactants having different HLBs, or mixtures of non-ionic surfactants with either anionic, cationic, or other surfactants, are all known.
A problem with surfactant-stabilized silicone emulsions is that they are sometimes prone to separation, which may be observed as an opaque phase (“creaming”) or an oily phase. Special mixtures and/or amounts of surfactants can sometimes alleviate this problem. A more difficult problem is separation due to temperature fluctuations, particularly freeze/thaw cycles. A third problem is the presence of the surfactant itself. Since surfactants necessarily have a hydrophilic component, this hydrophilic component, especially in emulsions having a large surfactant content, can cause unwanted water absorption after use, for example when used as a lubricating or surface-modifying component in compositions such as hard surface polishes. In addition, in some applications, surfactants simply cannot be tolerated at all.
To address these problems, so-called “self-emulsifying” silicones have been developed. Such self-emulsifying silicones can form stable emulsions with less surfactant, or even with no surfactant. Hence, the freeze/thaw stability is increased and water absorption/susceptibility is decreased.
Examples of self-emulsifying silicones are the aminoalkyl-terminated silicones, such as aminopropyl- or N-(2-aminoethyl)-3-aminopropyl-terminated polydimethyl siloxanes. Such amino-functional silicones can be prepared by hydrosilylation of, for example, an aminoalkene such as allylamine, with a silicone bearing hydrogendimethylsilyl terminal groups. When protonated, for example by an inorganic acid or organic carboxylic or sulfonic acid, etc., some degree of self-emulsification is achieved. The degree of self-emulsification decreases with increasing organopolysiloxane chain length. To achieve greater self-emulsifying properties, pendent aminoalkyl groups can be introduced along the polymer chain. There are several methods for incorporating pendent aminoalkyl groups, but these all require equilibration at some stage, and thus, the pendent aminoalkyl groups are randomly distributed.
In like fashion, functional silicones with full or partial self-emulsifying properties have been prepared by hydrosilylation to incorporate terminal and/or pendent glycosidyl groups, acryloyl or methacryloyl groups, or polyoxyalkylene groups. Silicones bearing internal, in-chain polyoxyalkylene groups have also been proposed. Silicones containing internal and pendent polyoxyalkylene groups have long been used neat as pore-stabilizing surfactants in polyurethane foam systems.
Such “self-emulsifiable” silicones thus either contained in-chain non-ionic surfactant groups, or pendent emulsifying groups which, again, were randomly distributed.
The random distribution of emulsifying groups in silicones is problematic. Not only are the emulsifying properties less predictable, due to the randomness of the placement of emulsifying groups, but in any mixture of such silicones, there will be a wide range of emulsification properties, even theoretically including some polymer molecules with few if any emulsifying groups. This characteristic may make aqueous emulsions more prone to separation, in particular, to creaming.
It would be desirable to provide self-emulsifying silicones with pendent emulsifying groups with regular, rather than random, positioning. At the same time, such self-emulsifying silicones should be capable of economic preparation, using commercially available or easily synthesized precursors.